Chalcedony was one of the unharnessed dragons recruited for Temeraire's regiment from the Pen Y Fan Breeding Grounds during Napoleon's invasion of Britain in December 1807. Along with Gladius, Chalcedony was chosen by the unharnessed Yellow Reapers as one of the best and most enthusiastic fighters to accompany Temeraire for what proved to be guerrilla warfare, while Cantarella was put in charge of the Reapers who stayed behind with the main force and given an epaulette to mark her rank.

Chalcedony was sometimes too enthusiastic. When the guerrilla forced attacked two Petit Chevaliers, Maximus killed one by falling directly on top of her. Chalcedony promptly tried to repeat Maximus' feat with the other Chevalier. However, Petit Chevaliers are heavyweights, smaller than Regal Coppers like Maximus but still considerably larger than a middleweight Yellow Reaper. The Chevalier simply bowled Chalcedony over, only to be caught in a torrent of flame from Iskierka - who almost hit Chalcedony as well.

Chalcedony fought bravely during the Battle of Shoeburyness in March 1808, although when reminded by Temeraire that it was his duty as an officer to keep the other Reapers in position, he rather cravenly pointed out that it was Cantarella who had the epaulette. (A remark of which Cantarella immediately took advantage.) In the end, Chalcedony's enthusiasm was to be his death. When the Britsh naval ships opened fire and the Reapers were supposed to be herding the French dragons into range of their cannons, Chalcedony pursued a Pou-de-Ciel too far. He took a cannonball in the chest and fell without a sound.

After the battle, the Yellow Reapers carried his corpse off the field. He was buried in the barrow-mounds on the old quarantine-grounds near the Dover covert, where the victims of the Dragon Plague had been laid to rest.

"Chalcedony" is a name for a class of quartz-based minerals, whose exact definition varies by technical field. Geologists include patterned and opaque stones such as onyx, agate, and jasper; jewelers prefer to limit chalcedonies to translucent stones of uniform color.